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## Proposal for Dealing with Low Emissions Stack Systems that Will be Excluded from Testing Under the Stack Test Option

. If a fab chooses to use the stack test option, it will test stacks that handle exhausts from fab manufacturing equipment (tools) using F

- gases. Stack t esting must account for a minimum of 85% of annual emissions determined in multiple ways including options such as :
U se the EPA update of Tier 2a method and the most recent year of F

- gas usage to calculate overall estimated F

- gas em issions. Allocate F

- gas usage to individual stack s ystems that are candidates for exclusion using the method described below and estimate emissions from those low stacks to demonstrate emissions are less than 15% of the total , or C ompare the estimated F

- gas emissions ( using Tier 2a method ) of the stack s ystem not being tested to the actual total fab F

- gas emissions from the prior year reported under Subpart I.

Proposal for Determining Gas Use Associated with “Low Emissions Stack Systems” That Are Not Being Tested A stack system is any set of stacks on a common header. If there is an interest in excluding from t esting one or more low F

- gas emission stack system s , t he fab will estimate emissions from each such stack system by iden tifying the number of F

- gas using manufacturing tools tied into each stack system

. F

- gas u sage for a given stack system will be allocated by multiplying the total fab usage of a particular F

- gas by the ratio of the number of tools using that F

- gas on the stack system to the total number of tools using the F

- gas in the fab. This will be done for each F

- gas to assign a portion of the F

- gas use to the stack system that might be excluded from testing. If a stack is excluded from testing, its F

- gas emissions will be determined using the updated Tier 2a factors in conjunction with POU abatement DRE factors . The F

- gas use assigned to any untested stacks will be deducted from the total fab F

- gas usage that will be used to determine the emissions factor s for the stacks that are tested.

Proposal for Addressing Low Use Gases and Non

- Detect Emissions Under the Stack Test Option
. Determining F

- Gas Use For Low Use F

- Gases (for use in determining emissions factors ) Gas usage is typically tracked using weigh scales or pressure transducers. If the usage of a n F

- gas is low , relative to the size of the supply cylinder or cylinder systems and it is not possible to determine usage during the test period with confidence fr om cylinder usage tracking, a number of approaches can be used including :

- U se a longer period of time (> than duration of stack test) to determine chemical usage. A period representative of the operation at the time of the test , and including the test per iod, will be used to estimate usage during the test period. This determination will be fully documented in the record of the det ermination of emissions factors; or2

- If a fab has the ability and chooses to, the fab may track F

- gas usage using a f lowmeter dur ing the test period; or

- For certain systems where multiple cylinders are ganged together to supply tools, it may be possible to supply the gas from just a single cylinder for the duration of the test. However, this alternative will only work in certain sit uations. Determining E mission F actors f or G ases that are not D etected or They are Detected Infrequently during the Stack Test T h e following protocol will apply:

- If an F

- gas is used but emissions are not detected , calculate the emission factor by assuming emissions at 1⁄2 Field Detection Limit (F DL ) of the specific gas and dividing by total usage of that gas

.

- If an F

- gas is used and detected (for some portion of the test period ) , calculate emissions using detected quantity for the time when it is detected and 1⁄2 F DL when not detected and divid ing by total use of that F

- gas. If calculated EF is greater than 1.0, assume EF=1.0.

- If an F

- gas is not used and no emissions are detected , assume emissions are zero.

- If an F

- gas is not used but it is detected (for some portion of the test period), calculate emissions , as a by

- product, using detected quantity and 1⁄2 F DL when not detected and divid ing by total F

- gas usage.

- If an F

- gas is not used during the test period but is used duri ng the reporting period, emissions will be estimated using the Tier 2a method

.